1. Field of the Invention
The present invention relates generally to a sheet guide positioning apparatus and more particularly to a sheet guide positioning apparatus which when the width of a corrugated cardboard sheet conveyed at high speeds is changed, is suitable for instantaneously changing the spacing between a pair of sheet guides which guides the sheet therebetween in accordance with the changed width of the cardboard.
2. Prior Art
Generally, in manufacturing a double-sided corrugated cardboard sheet, as shown in FIG. 4, single-sided corrugated cardboard sheets 1, 2 manufactured by single facers are temporally stored on overhead bridges 3, 4 in a zigzag manner, conveyed by conveyors on overhead bridges 3, 4 and fed to a preheater 8 on the side of a double facer 7 via vacuum brake devices 5, 6. Vacuum brake devices similar to the vacuum brake devices 5, 6 are disclosed in Examined Published Japanese Patent Application No. 56-32098. The vacuum brake devices 5, 6 disclosed in the application have vacuum chambers 9, 10 which suck the liner sides of single-sided cardboard sheets such as those shown in FIG. 4 toapply tension to them. When the widths of the single-sided corrugated cardboard sheets are changed, the widths of the vacuum chambers 9, 10 are arranged to be adjusted to correspond to the changed widths of the cardboard sheets. The vacuum brake devices 5, 6 have two pair of sheet guides 11, 12 which guide therebetween the cardboard sheets 1, 2, respectively. The spacing between each pair of sheet guides 11 or 12 is adapted to be changed in conjunction with adjustment of the width of the corresponding vacuum chambers 9 or 10. The mechanism which adjusts the spacing between each pair of sheet guides 11 or 12 includes a screw rod consisting of half portions having mutually opposite threads thereon. The sheet guides 11 or 12 of each pair are screwed onto the corresponding opposite threads so that when the screw rod is rotated, the spacing between the sheet guides is adjusted so as to correspond to the width of the corresponding sheet 1 or 2. Because of this, the spacing between each pair of sheet guides 11 or 12 can not be adjusted instantaneously from one value to another corresponding to the next different width of the sheet. Especially, in order to adjust the guide spacing from its maximum to its minimum and vice versa, much time is required. Recently, the single-sided cardboard sheets 1,2 will be conveyed at high speeds especially in order to improve the manufacturing efficiency per hour. Thus, since a certain time is required to adjust the spacing between the sheet guides 11 or 12, and when the next portions of the cardboards 1, 2 have greater widths than the preceeding portions, adjustment of the spacing between each pair of the guides 11, 12 must be started before the leading edge of the different width portion of the corresponding cardboard 11 or 12 arrives at the corresponding sheet guides 11 or 12, and when the adjustment has been completed, the leading edge of the different width portion of the cardboard sheets 1 or 2 must arrive at the corresponding sheet guides 11 or 12. Otherwise, the leading edge of the different width portion of the cardboard sheet 1 or 2 would be hit against and damaged by the corresponding sheet guides 11 or 12. As a result, when the spacing between each pair of sheet guides 11 or 12 is adjusted, the corresponding cardboard sheet 1 or 2 is not guided properly at all. As a result the sheet 1 or 2 may be conveyed unsteadly out of position. Thus, in bonding the single-sided cardboard sheets 1 and 2 and then a liner sheet 13 to them, the cardboard sheets 1, 2 and the liner are displaced one from the other, thereby resulting in a bad product in which the cardboard sheets and liner are uneven in edge. In addition, it is not easy to take the timing of adjusting the sheet guide spacing to the next different width portion of the sheet.
In order to eliminate these problems, applicant has proposed a single-sided corrugated cardboard sheet guide apparatus, which is disclosed in Examined Published Japanese Utility Model Application No. 57-29320.
This apparatus has a pair of upper and lower sheet guide mechanisms, each including a pair of sheet guides which guides therebetween a single-sided corrugated cardboard sheet. While one pair of sheet guides is guiding therebetween a single-sided corrugated cardboard sheet, the other pair of sheet guides is adjusted in advance so as to correspond to the next different width portion of the cardboard sheet produced according to different order. When the different width portion of the cardboard sheet arrives at the one pair of sheet guides, guiding is switched instantaneously from the one of pair of sheet guides to the other pair, using air cylinder means. Since, in this apparatus, switching is instantaneously performed from one pair of sheet guides to another pair when the width of the corresponding single-sided corrugated cardboard sheet is changed, the sheet can be guided continuously, but a pair of upper and lower sheet guide mechanisms is needed. Thus, although this apparatus has a simple structure, the entire apparatus becomes large-scaled, occupies a large space and becomes large-sized.